I have about £1000 to spend but thats the max

I live near the south west coast and photograph wildlife mostly, birds,deer, flowers etc.
Geoff, your right if i have the lens already then it would make sense to buy Nikon. One of the shops i went to told me the D90 has a motor in its body and i'm not sure if i'll be able use my existing lens?? its a Sigma 70-300mm.
The pics ive currently got exhibited had to be quite large and so the pic quality isnt as good as i would like. with my upgrade i would like,
a) better pic quailty
b)the ability to use a 400/500mm lens (if i can afford on after buyng the camara!) or digiscope.
my knowledge is very limited and all the tech talk you get from the shops confuses me.
hope this is of help

Sandymere